1. Field of the Invention
The present invention relates to a recoder, and more particularly to a serial printer type recorder which can precisely feed a record medium.
2. Description of the Prior Art
Various recorders such as a wire dot printer and an ink jet printer which print characters with a recording head having a plurality of recording elements while moving the recording head widthwise of a record medium.
Those recorders are widely used as image printers because they can print not only characters but also patterns and lines using dots.
However, image recording by such recorders is not always of high quality.
For example, when an image is recorded by a wire dot printer having seven wires as shown in FIG. 1A, if paper is fed too much, a gap is created between an upper row of seven dots and a lower row of seven dots in adjacent lines.
Conversely, if the paper feed is too less, the upper dots and the lower dots overlap as shown in FIG. 1B and a dark double-print area 2 is created.
Thus, a gap area or double-print area is created by the error in the paper feed.
In order to avoid the above problem, a slip between the record medium and the feed roller should be zero and the record medium should always be fed by an exactly constant amount which is impracticable.
For example, if a record paper 3 is obliquely set in the recorder as shown in FIG. 2, the record paper 3 is gradually shifted left as shown by chain lines for each paper feed even if the paper is fed in a direction of an arrow without slip, and eventually contacts edge 4 of the recorder and jams.
In prior art recorders, the jam is prevented in the following manner, at the sacrifice of the quality of the image recording.
In one method, a longer paper guide than the paper width is provided to minimize skewing of the record paper. In another method, a paper feed roller is designed to slip when a heavy load is applied thereto so that the direction of the paper feed is changed by the increasing load when the record paper contacts to the edge of the recorder.
The latter method is explained with reference to FIG. 3.
Numeral 8 denotes a locus showing the feed direction of the record paper 3 in an exaggerated manner, and numerals 5-7 denote positions at which the record paper 3 contacts an edge.
If the paper feed direction is changed, the record paper necessarily snakes; the smaller the difference between the width of the paper guide and a width of the paper and the longer the paper guide, the smaller the amount of snake. In practice, however, the size of the record paper is not exact, and in a recorder which uses wide record papers, the recorder will be of large size of the paper guide width is increased.
As a result, the gap or the double print occurs at the contact points 5-7.
When wider record papers or thin record papers are used, they cannot be even snaked and thus jam at the first contact point 5.